Zinc and the common cold

cold-eezeShortly after I developed sore throat, cough, and congestion last week, a package of ‘Cold – Eeze’ materialized on my kitchen counter. The writing on the package of zinc-laden lozenges promised to ‘shorten your cold’, and noted that they were ‘clinically proven to reduce the duration of the common cold’. Do zinc lozenges have any effect on the common cold?

The common cold is the primary cause of doctor visits in the United States, leading to 189 million lost school days each year. But it’s important to point out that the common cold can be caused by a number of different viruses, including rhinovirus, coronavirus, influenza virus, adenovirus, and paramyxovirus. Rhinoviruses are responsible for over half of all common colds.

The idea that zinc could be used to treat the common cold originated from a 1974 paper in Nature which showed that zinc blocks the replication of rhinoviruses in cell culture. Viral plaque formation was inhibited over 99% when 0.1 millimolar zinc chloride was included in the agar overlay. However, this concentration of zinc is too high for therapeutic use, and subsequent studies showed that levels compatible with use of the metal ion in humans minimally inhibited rhinovirus replication in cell culture. Zinc does not readily pass through the cell membrane, explaining why high concentrations are required to produce an antiviral effect.

Many trials have been conducted to determine if zinc – taken as a lozenge, nasal spray, or ointment – has any effect on the common cold in humans. In one study, 200 children were given 15 mg zinc daily by mouth for seven months. The mean number of colds in the treated children was 1.2 compared with 1.7 in the untreated children – statistically significant but not therapeutically useful. Many studies have evaluated the effectiveness of zinc containing lozenges. In one, 65 people took one lozenge containing 23 mg zinc every two hours while awake. After one week, 86% of the treated group were free of cold symptoms, compared with 46% of the placebo group. In another similar study, the duration of cold symptoms was reduced in the zinc group versus the placebo group – 4.5 days compared with 8.1 days. However, as many studies have lead to the conclusion that zinc lozenges – as well as zinc administered intransally or in a gel – have no effect on severity or duration of the common cold. A good summary of many of these trials can be found in the Alternative Medicine Review cited below.

It’s important to note that in these studies the virus responsible for the colds is not identified. Given the prevalence of rhinoviruses it is appropriate to assume that these viruses are involved in over half of the colds observed. Nevertheless, the extreme variability in the trial results may in part reflect the fact that various etiologic agents are involved, some of which might not be susceptible to inhibition by zinc. Other possible explanations for the inconsistent results include differences in the zinc preparations used (zinc gluconate and zinc acetate), the quantity of zinc administered, and the composition of the lozenge.

Although inhibition of rhinovirus replication by zinc was reported in 1974, the mechanism is not understood. It is believed that zinc enters the cell and binds to the rhinovirus protein that will form the capsid. This interaction blocks cleavage of the protein, thereby inhibiting production of infectious virus. Consistent with this proposed mechanism is the observation that zinc ionophores – compounds that allow the uptake of zinc into cells – have recently been shown to inhibit rhinovirus replication. The effectiveness of such compounds, which include pyrithione and hinokitiol, for treating the common cold is currently being investigated.

Although zinc does inhibit rhinovirus replication, this activity might not account for the effect on the common cold. It has been suggested that zinc reduces inflammation in the respiratory tract, which would explain the observed decrease in symptoms observed in some trials.

As for the Cold-eeze on my kitchen counter – the package was never opened. The unimpressive results of clinical trials made the idea of taking 6-8 lozenges a day for several days less appealing than enduring sore throat, cough, and congestion for less than a week. But the lozenges served a different purpose – I am now very interested in the revealing the mechanism of zinc inhibition of rhinovirus replication. I have begun experiments in my lab to solve this problem, and I’ll write about what I discover.

Korant BD, Kauer JC, & Butterworth BE (1974). Zinc ions inhibit replication of rhinoviruses. Nature, 248 (449), 588-90 PMID: 4363085

Geist FC, Bateman JA, & Hayden FG (1987). In vitro activity of zinc salts against human rhinoviruses. Antimicrobial agents and chemotherapy, 31 (4), 622-4 PMID: 3038000

Krenn, B., Gaudernak, E., Holzer, B., Lanke, K., Van Kuppeveld, F., & Seipelt, J. (2008). Antiviral Activity of the Zinc Ionophores Pyrithione and Hinokitiol against Picornavirus Infections Journal of Virology, 83 (1), 58-64 DOI: 10.1128/JVI.01543-08

Roxas M, & Jurenka J (2007). Colds and influenza: a review of diagnosis and conventional, botanical, and nutritional considerations. Alternative medicine review : a journal of clinical therapeutic, 12 (1), 25-48 PMID: 17397266

20 thoughts on “Zinc and the common cold”

  1. If I recall correctly, Cold-eeze is even sillier than the average zinc treatment; it's a homeopathic “remedy” in which the average lozenge does not actually contain any zinc. It's just sugar, dye, and a little flavoring.

  2. Youre right, Treppenwitz, it even says “homeopathic” on the label pictured above. What a crock.

  3. Can't wait to hear the results! What sort of experiments are you going to try. Now you have me wondering about my viruses.

  4. I don't have the package with me but the cover reads 'zinc gluconate' which is one of the zinc salts used in the trials. I'll check the contents list when I'm home.

  5. I plan to see if zinc inhibits several different rhinovirus serotypes as reported. If so I will try to isolate zinc-resistant mutants and determine the responsible mutation. This analysis should provide clues about the mechanism of action of the metal salt.

  6. The active ingredient is listed as “Ionic Zinc (13.3 mg) from Zincum Gluconicum 2x.” It's unclear whether they're claiming to have 13.3mg of zinc or 13.3mg of homeopathic dilution, i.e. 13.3mg of .01mol/L solution.

  7. I've always shied away from zinc medications because of the (rare) reported cases of induced anosmia. While it may be rare and due to a pre-existing genetic factor, I don't want to risk my sense of smell for a common cold.

  8. I've always shied away from zinc medications because of the (rare) reported cases of induced anosmia. While it may be rare and due to a pre-existing genetic factor, I don't want to risk my sense of smell for a common cold.

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  10. You should have tried them. At the first sign of a cold I take them (only 3 a day). I haven’t had a cold that lasted more than 2 days in years.

  11. Robertbauman

    There are reports the body builds immunity to colds, one by one.  Therefore, with age I feel “immune” to most colds; i.e., going to bed for a few hours clears nearly every cold within 24 h.
    I haven’t yet tried Zn.

  12. Jay Turberville

    Yep. My personal experience is that they seem to work. I try to take three, one right after the other at the first sign of a scratchy throat – letting them dissolve as slowly as is practical. The sooner I take them the better the results seem to be. I then take them as directed on the package. I’m usually fine within 24 hours. After a day or so, I stop taking them whether I’m better or not. That’s a lot of zinc to ingest in a 24 hour period of time.

    Anecdotal, for sure. But even if it is purely a placebo affect, that’s OK with me. Cost is low. Risk is low. They don’t taste bad. They do leave a weird taste in your mouth. But a bad cold makes food hard to taste anyway.

    BTW, the homeopathy labeling is simply the maker using a loophole that allows them to market the lozenge as a “remedy” with minimal FDA restrictions. This isn’t a homeopathic remedy with super-scarce trace “active” ingredients. At least one other maker took their zinc lozenge off the market when the FDA required them to either change their labeling and claims or to market their lozenge as “homeopathic.”

  13. I can’t imagine why you wouldn’t at least try it – what do you have to lose? Being ill, contagious, with a suppressed immune system doesn’t seem like a great response.

  14. I can’t say for sure because I cannot create an alternate universe wherein I don’t take them, but Cold-Eze seem to work for me sometimes, and sometimes not. (Could be I’m fooling myself, I dunno.) I’m sucking on one right now trying to stave off a sore throat I developed last night.

    (Another downside to using them: they cost around $5 for 18 lozenges.)

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